Fault Analysis of a Transformer Tripping and Protection Rejection

Two-phase ground short circuit occurred on 35kV side of main transformer in a 220 kV substation. The low voltage side 301 circuit breaker did not jump off. Then the differential protection of the main transformer is started, which causes tripping of the three sides of the main transformer and no load loss. In this paper, the primary equipment, secondary equipment and monitoring background information related to the fault are investigated and analyzed in detail, and the causes and development process of the fault are restored. Because of the special fault, in order to avoid the similar situation happening again, some suggestions are put forward for the improvement of the merged intelligent device.